This invention relates to a photosensitive material containing a silver halide emulsion layer stabilized against overdevelopment fogging.
When a silver halide photosensitive material is treated for a very short period of time under severe developing conditions, such as development at a relatively high temperature or development with a highly active developer (a developer at a high temperature and a high pH), there arises a danger of the reduction of silver halide grains containing no latent image nucleus at all. The fog produced under such conditions by the undesirable reduction of undeveloped silver halide grains strongly appears especially at the end of a normal development process and is called overdevelopment fog. The antifoggants known to be effective against the overdevelopment fog include mercury compounds and heterocyclic mercapto compounds. These antifoggants reduce the fogging in a normal developing treatment or in overdevelopment. They have, however, a disadvantage of appreciably reducing the sensitivity of a silver halide photosensitive material when added in an amount sufficient for the reduction of such fogging.
The fundamental disadvantage of adding directly to the silver halide emulsion a heterocyclic mercapto compound particularly active in itself against the overdevelopment fogging lies in that such a compound is perfectly active from the time of addition, namely, it is already in active form throughout the storage period of the photographic material and in the development stage. As a consequence, it exerts an undesirable desensitizing effect during the manufacturing and storage of a photographic material. In order to avoid such a difficulty, an attempt was already made to substitute the mercapto group of the antifoggant compound by a suitable hydrolyzable group so that it may become possible to inactivate the antifogging activity during the period (including the manufacturing period and succeeding period before the development stage) in which such an activity is not desired and then in the development stage regenerate the active form by alkaline hydrolysis. Such substituted compounds are thioesters and thioethers of the mercapto antifoggants. The thioesters are those of carboxylic acids, sulfonic acids and carbonate derivatives disclosed in many patents such as, for example, German Pat. No. 1,597,503, U.S. Pat. No. 3,260,597 and German Patent Application "Offenlegungsschrift" No. 2,061,972. The thioesters, however, have a disadvantage in that although being hydrolyzable in alkaline developer media, they also gradually undergo partial hydrolysis in neutral or weakly acidic pH range. Therefore, although the thioester-type antifoggants can be added in inactive form as such to an emulsion, they exert an undesirable desensitizing effect due to partial hydrolysis when quite an extended time is required in the manufacture of emulsion or storage of the photographic material. In contrast to the thioesters, the antifoggants having a substituent of the thioether type, such as those disclosed, for example, in U.S. Pat. Nos. 2,981,624 and 3,260,597 and German Pat. No. 1,173,796, are quite stable in neutral or weakly acidic media, but are unable to prevent effectively the overdevelopment fogging, because they do not regenerate or regenerate very slowly the original mercapto antifoggants in the development process.